Posted
by
Soulskill
on Wednesday March 28, 2012 @01:23AM
from the working-their-way-up-to-cat-sized-objects dept.

An anonymous reader tips news that researchers have successfully demonstrated particle-wave duality in molecules that have masses of 514 and 1,298 atomic mass units. The academic paper can be found in Nature Nanotechnology.
"Thomas Juffmann et al. fired molecules composed of over 100 atoms at a barrier with openings designed to minimize molecular interactions, and observed the build-up of an interference pattern. The experiment approaches the regime where macroscopic and quantum physics overlap, offering a possible way to study the transition that has frustrated many scientists for decades. ... The relatively large phthalocyanine (C32H18N8) and derivative molecules (C48H26F24N8O8) have more mass than anything in which quantum interference has previously been observed. To have wavelengths that are relatively large compared to their sizes, the molecules need to move very slowly. Juffmann et al. achieved this by directing a blue diode laser onto a very thin film of molecules in a vacuum chamber, effectively boiling off individual molecules directly under the beam while leaving the rest unaffected. ... The researchers observed the particle nature of the molecules in the form of individual light spots appearing singly in the fluorescent detector as they arrived. But, over time, these spots formed an interference pattern due to the molecules' wavelike character.'"

Funny, but I'll answer anyway.:-) No, of course it hasn't. Yes, you could say that it exhibits particle-wave duality without trying it. Regardless, Schroedinger's Cat is about superposition of states and not particle-wave duality.

Scientists are currently trying [sciencemag.org], albeit with somewhat smaller objects than a person. What you should understand is that the tunneling probability is exponentially damped in both the width of the barrier and the size of the object.

Already for a hydrogen nucleus tunneling through the (electrostatic) potential barrier presented by another hydrogen nucleus, the probability is around 10^-30 (if memory serves correctly). This fact is what keeps the sun burning for billions of years, and not exploding like a hydrogen bomb in a split second, since it limits the rate of fusion processes in the sun.

Alright, let me clarify what I meant. In fusion, the main factors in determining the reaction speed is the energy and the density. While the energy is comparable in the sun and a hydrogen bomb, the density is 2 orders of magnitude higher in a hydrogen bomb than at the sun's core. The tunneling probability is exponentially sensitive to the density; so sensitive that a third of the way out from the sun's core, fusion can no longer happen. This means that those 2 orders of magnitude are translated into 20 orders of magnitude slower explosion. At that point, I wouldn't call it an explosion.

Just to highlight this point: the power production per volume at the sun's core is 280 W/m^3. This is less than for a human being, it's roughly the same power as a crocodile produces per volume.

TL;DR: You're saying that the smoldering pile of flour on my kitchen bench is exactly like a dust explosion. I beg to differ.

I should point out that for sufficiently small objects, scientists already do this on a regular basis. Scanning tunneling microscopy, for example, relies on electrons tunneling through a potential barrier, using the tunneling rate to measure the strength of the barrier. (Strictly speaking, small-scale electron tunneling is happening all the time, everywhere, but that doesn't make for a good concrete example.)

In theory, you could do it with an entire chromosome since these have bonds connecting the entire structure in some way, but the problem is that the wavelength is proportional to it's mass and for something like a chromosome, you're dealing with something with an atomic mass on the order of billions of AMU. This isn't really too big of a problem, the issue comes from that larger molecules have other interactions that interfere with the measurement. A segment of DNA for instance consists of the deoxyribose d

It would be very difficult to test DNA in the manner described in the paper- it would appear that the specific molecules chosen have a number of attributes that make them suitable for the double-slit experiment. They are fluorescent dyes, which makes them very sensitive to detection, they can be vaporized without thermal decomposition, they are neutral molecules, and they have multiple symmetries so that there isn't a preferred orientation. DNA molecules would be destroyed by the heat sources they used, and the highly charged DNA molecule is likely to interact with the atoms of the diffraction grating in a classical electrostatic manner.
Some other biomolecules might be more suitable- phthalocyanine is similar in structure to heme and chlorophyll.

I believe the difference from the fullerene is that they are detecting the single particles here, instead of a stream. In this sense they can really show that each particle interferes with itself, since while one molecule travels to the screen there is no other particle to interact or interfere with.

This should happen with everything, it just happens to be that larger objects are going to very difficult to isolate from noise (which causes "decoherence"). What is impressive about this experiment is the degree to which the experimentalists were able to isolate this system from external interference (and move them so slowly), not that larger objects happen to exhibit QM properties (this is completely expected).

Among the last few generations of physicists it is generally believed that everything is quantum from an elementary particle to whole planets. It's just very difficult to cool planets down to where the thermal length is smaller than their de Broglie's length. Not to mention creating a coherent planet gun and detector... But there was no reason to believe it is fundamentally impossible.

Wave particle duality had already been demonstrated on Buckyballs which have a collective molar mass of 720. Here's an article is from 1999 : http://physicsworld.com/cws/article/news/2952 [physicsworld.com]
OK, these are larger molecules rather than the larger particles in the new research, but what's being presented here isn't so much of a leap... is it?

It's hard to be "turbulent" when there is only one molecule in flight, in a vacuum. I believe that the idea here is that although the molecule can only pass through one of the slits in the grating, it behaves as if it passed through all of the slits simultaneously and interfered with itself on the way through, thereby affecting the probability of where it strikes the detector.

As opposed to anything larger than a photon, at first. The famous "dual slit" experiment. Then electrons, in the understanding of photovoltaic effect. Protons and Neutrons are quite a bit larger, and atoms larger yet. Then molecules of the same atom (buckyballs). Now we have a particle, with combinations of different atoms.

For most people who know anything about this duality, they learned about the dual-slit experiment, so your most common answer is likely to be "photon", the "quantum of light" and the

I'd have more confidence in your opinion if you said something like "I find Feynman's path integral formulation more convincing". I guess it's just a matter of word choice but "I believe in" doesn't really sound like someone who's making a rigorous analysis of the evidence.

It's great to study, understand and use Feynman's path integral, especially since it leads to new insights about the nature of Quantum Mechanics (plus, seeing the familiar face of the principle of least action in the quantum world is just awesome). But it seems counter-productive to limit yourself to it. For example, some problems that are relatively simple to solve using the "usual" methods (i.e., thinking about waves and using the Schrodinger equation) can become intractable math nightmares with Feynman's path integral. I'm sure there are problems for which the reverse is true, too.

Most people who work with QM seem to take a very pragmatic approach when dealing with problems outside the foundations of QM: use whatever works for you for the problem at hand. Peter Shor (the guy who invented the quantum algorithm to factor numbers in polynomial time) once wrote:

Interpretations of quantum mechanics, unlike Gods, are not jealous, and thus it is safe to believe in more than one at the same time. So if the many-worlds interpretation makes it easier to think about the research you’re doing in April, and the Copenhagen interpretation makes it easier to think about the research you’re doing in June, the Copenhagen interpretation is not going to smite you for praying to the many-worlds interpretation.

It was a terrible analogy to begin with, not an argument. And you are correct that he argued one side but forgot the other.

It was more of an excuse to take a a jab at multitheism, if not deism completely, and I'm sure there are better ways to explain it without inserting personal bias.

The premise probably included the assumption that since people have believed both ways, neither one could be called the correct way. This is the scientific method, if contradictory results are observed no conclusion can be m

For example, some problems that are relatively simple to solve using the "usual" methods (i.e., thinking about waves and using the Schrodinger equation) can become intractable math nightmares with Feynman's path integral. I'm sure there are problems for which the reverse is true, too.

Which is why we have this Schrödinger-Feynman duality to explain the whole..;)

There is no particle-wave duality. Every particle is only a wave and sometimes, if you look from very far (or at high temperatures) it seems to behave as a point-like object.

In any case it is not like path integrals are alternative to the normal schroedinger wavefunction formulation. See the work of Dyson for that, or simply the Feynman-Kac formula. At the fundamental level path-integrals ar just combinations of double-slits experiments in a very abstract space (Trotter's formula).

And yes, in the path integral a particle interferes with itself. You'll notice that you have to take into account and sum paths going through different slits.

I do work in the path integral formulation because I think it is more elegant, but it is not an alternative to the "traditional" wavefunction approach (hey, path integral is not exactly new anymore). It is the same as choosing cartesian or spherical coordinates.

I do not believe in particle-wave duality. I believe in Feynman's path integral formulation.

This is not related in the way you might think it is. The former is a philosophical problem in the interpretation of quantum mechanics, the latter is one of several ways of resolving this problem in practice.

Particle-wave duality is not philosophical. What it means and whether an object "really" is both a particle and a wave might be philosophical questions, but that's not what's meant in physics when one refers to "particle-wave duality". It's the observable (and, indeed, observed) fact that objects exhibit a set of properties that are both classically wave-like and classically particle-like.

In modern quantum mechanics you don't even really talk about particle-wave duality much. It's simpler to approach it fro

We're not that far apart. I meant it in the sense that it is an empirical phenomenon that poses a problem in the interpretation of QM. The concept is philosophical in the sense that it is rather used by philosophers or teachers and not so much by practicing physicists.

I do not believe in particle-wave duality. I believe in Feynman's path integral formulation.

This is total nonsense. You might as well say that you don't believe in addition, you believe in electronic calculators instead. A calculator is one method for adding numbers. The Feynman path integral formulation is one method for doing calculations in quantum mechanics, which has wave-particle duality.

IANAAP, but I once heard everything has a base frequency (not mechanical, but something else, based on the mass of the object). With the speed of the cat this results in a wavelength. I'd guess the maximum slit size is connected to the resulting wavelength (a to wide a slit would not give an interference pattern). The question is: how fast do we need to launch the cat (using a catapult of course) to get the wavelength long enough to make the maximum slit wider than the cat?

You can have a photon with half the energy of another photon, but you cannot have half a photon.

Ill try another tact....If you had a hole, and filled in half of it, you would be left with a hole. There is no such thing as half a hole, but there is such thing as a hole half the size of another hole.

Not the best analogy, but it all boils down to one simple fact. A quantum of light ( a photon ) is the smallest unit of light.

But a photon is not a wave. In fact, there is nothing waving. It is the electromagnetic field that changes state. So it should be possible to represent a photons electromagnetic state change through space as a series of dominos falling, one after the other, carrying energy as it goes. In that case, it's actually a quarter wave, where the velocity is determined by how close the dominoes are to each other. This "domino spacing" changes depending on the density of "vacum space" which is clearly dependent

If there's no way you or anyone else can detect a "half photon" - i.e. if it doesn't have any observable effect on the universe whatsoever - then it only exists in a sense that the Invisible Pink Unicorn exists.

I think it would be much simpler to tell GP about the photoelectric effect, where it is clear that the energy of a beam of light comes in a multiple of indivisible units, just like electric charge comes in multiples of indivisible units.however, I think the GP was just trolling, so I'm not going to bother with the details.

Wave-particle duality has yet been observed with much bigger objects, on different physical basis but with astonishingly equivalent behaviour.

A 'walking' drop on a liquid surface behave like a particle with wave properties: diffraction, interference patterns, vibration quantization.

First, in a vibrating container they put a liquid like silicon oil, vibrations are just bellow the Faraday instability threshold. Then a drop of the same liquid is dropped on the surface, but it does not coalesce, it bounces. And further bounces make a static wave pattern on the liquid surface just bellow the drop and its immediate neighborhood. As the spike grows, instability increases and the drop slides down the spike, and start moving horizontally.

Then they have a combo object drop+wave pattern moving at 1/10th the speed of wave in this liquid, straight. They call it a walker.

What is really amazing is that the wave pattern below the drop has some kind of memory: it has accumulated energy from several drop bounces. It can also make the drop see "forward", as the small wave pattern bounces back from nearby obstacles. So the drop is "aware" of its environment and "recall" the path it has followed.

Diffraction is observed and explained by the multiple reflexions the wave makes when the drop passes through a small hole, randomizing the wave pattern and the angle of the path afterward. Interference patterns observed are explained a la de Broglie: as the drop passes through one of the two holes, its associated wave passes through both, carrying forward the message of the second hole to the drop and changing the statistical repartition of the drop's path direction. One more stunning result: they are circling the drop by moving the container (Coriolis), then the associated wave adopts a discrete series of pattern, depending on the speed and radius. Very much like the energy quantization of electrons.

umm... the research you're talking about, while interesting, is not an example of quantum phenomena.the message of the article discussed here is "matter behaves in the weird quantum way even when you're talking about molecules". i.e. "we made an experiment with real molecules, and they act as predicted by quantum mechanics". it is a verification of theoretical predictions, with the purpose of strengthening our belief that quantum physics is "true". it is conceivable, while unlikely, that they would have obtained different results, thus implying that the passage from the quantum world to the macroscopic world is much more complicated then we currently believe.the message of the thesis you link to is "with a properly set up classical experiment, we can reproduce quantum physics behavior". even if the molecules of liquid are described by classical physics, once you put a drop on a surface that vibrates very rapidly, you will observe that the drop bounces, and it is being carried by a wave on the surface of the liquid. by design the particle is carried by a wave, but only classical physics is relevant. they do talk about quantum physics because (in a somewhat funny situation) the simplification of the classical physics leads to equations that resemble those in quantum physics. it's just like you can write the same equations to describe sound and radio waves, even though the reasons sound waves exist are completely different from the reasons radio waves exist.

We know that water waves are composed of watr molecules, and electromagnetic waves are composed of electrons or photons.

What is a quantum particle wave composed of?

The waves in the ocean have very little to do with the water. The waves are as a result of the forces acting on the water (wind, tides, probably air/water surface friction, etc).

heat waves are composed of air moledcules

The heat has nothing to do with the air. What you experience as heat is the release of energy as photons from the moving air molecules. The air is moving, but it is the release of the photons is the cause of the heat.

Your car gets hot in the sun because the car absorbs many photons of energy. You get burned when you touch your hot c

Electromagnetic waves aren't composed of electrons at all. Electromagnetic waves are composed of photons in the sense that the photon is, by definition, the particle representation of an electromagnetic wave or, equally, the force-carrier for the electromagnetic force.

In the same sense, what "composes" the quantum wavefunction of an electron is an electron. What composes the quantum wavefunction of an up quark is an up quark.

The dual slit experiment reminds me of Frost's poem, "The Road not Taken." Even though you take a fork in the road you will know you could have taken the other road and wonder what would have happened if I took the other road. If the path was blocked then you wouldn't wonder about it.

It is wrong to assume that making correct predictions results in the correct understanding of your subject.

How do you scientifically distinguish "correct" understanding from "incorrect", if both have the same predictive power?

Earth being flat was giving correct predictions only within very narrow boundaries, and was quickly falsified - pretty much any predominantly seafaring culture (like ancient Greeks) knew Earth had to be round based on their observations.